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LM3429: PWM frequency

Part Number: LM3429


Is there a limit to the PWM frequency input to the nDIM pin?
The customer plans to input a 12MHz PWM signal.
Although the LED is blinking, I think that the device is  not able to respond because the load varies widely.

Is there a device that can support high-speed PWM signals?

Best regards,
Yuto Sakai

  • Hi Yuto,

    No, the part will not run PWM dimming at 12MHz and I do not know of any LED current driver part that can PWM dim at that frequency.

    Thanks Tuan

  • Hi Tuan-san,

    Thank you for your reply.
    What is the expected PWM frequency input to the LM3429? Is there a max value?

    Best regards,
    Yuto Sakai

  • Hi Yuto-san,

    The max pwm frequency input into the LM3429 frequency also depends on the power stage design, compensation and load.  The PWM dimming for the LM3429 is really meant for really low dimming frequency of 1KHz or less and also the duty cycle of the dimming.  The reason for this it that the PWM dimming does not disconnect the LED load from the output and thus the output voltage will drop during PWM dimming OFF.  When the ON is commanded the power stage has to charge the output caps up to some level before the current can start flowing in the LED.  This will not be able to support your MHz dimming requirement at all.

    Thanks Tuan